MUC1 and small cell lung carcinoma: Although dominant molecular subtypes can be distinguished in most cases in SCLC, there is often significant heterogeneity in pathology and phenotypic switching may occur.[81] It has been found that SCLC‐A subtype can be converted to SCLC‐N subtype and further to SCLC‐I subtype under MYC drive.[82, 83, 84] Single‐cell sequencing analysis shows that MUC1 expression is the most prominent in the SCLC‐A subtype and normal epithelial stromal cells (Figure 1E–G).